MEMS Structures and Methods for Forming the Same

ABSTRACT

A method includes forming a MEMS device, forming a bond layer adjacent the MEMS device, and forming a protection layer over the bond layer. The steps of forming the bond layer and the protection layer include in-situ deposition of the bond layer and the protection layer

BACKGROUND

Micro-electro-mechanical system (MEMS) devices may be used in variousapplications such as micro-phones, accelerometers, inkjet printers, etc.A commonly used type of MEMS devices includes a MEMS capacitor that hasa movable element as a capacitor plate, and a fixed element as the othercapacitor plate. The movement of the movable element causes the changein the capacitance of the capacitor. The change in the capacitance maybe converted into the change in an electrical signal, and hence the MEMSdevice may be used as a micro-phone, an accelerometer, or the like. Themovement of the movable element may also be used in an inkjet printerfor squeezing the ink.

MEMS devices typically require a cap capping the MEMS devices forprotection purpose. The bonding may be performed through eutecticbonding. However, the bonded surface may have an oxide layer thatadversely affects the reliability of the bonding, and the oxide layerneeds to be removed before bonding.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 6 are cross-sectional views of intermediate stages inthe manufacturing of a micro-electro-mechanical system (MEMS) device inaccordance with various embodiments; and

FIGS. 7 through 12 are cross-sectional views of intermediate stages inthe manufacturing of a micro-electro-mechanical system (MEMS) device inaccordance with various alternative embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A micro-electro-mechanical system (MEMS) device and the method offorming the same are provided in accordance with various embodiments.The intermediate stages of forming the MEMS device are illustrated. Thevariations of the embodiments are discussed. Throughout the variousviews and illustrative embodiments, like reference numbers are used todesignate like elements.

FIGS. 1 through 6 illustrate cross-sectional views of intermediatestages in the formation of a MEMS device in accordance with someembodiment. Referring to FIG. 1, substrate 20 is provided. In someembodiments, substrate 20 is a semiconductor substrate such as a siliconsubstrate, although other semiconductor materials such as silicongermanium, silicon carbon, III-V compound materials, and the like may beused.

Active devices 22 such as complementary metal-oxide-semiconductor (CMOS)devices may be formed on a surface of semiconductor substrate 20. Metallayers 24, which include metal lines 26 and vias 28 formed in dielectriclayers 30, are formed over substrate 20 and active devices 22. Activedevices 22 are electrically coupled to metal lines 26 and vias 28 inmetal layers 24. Metal layers 24 include bottom metal layer M1 throughtop metal layer Mtop, wherein the symbol “top” represents the number ofthe topmost metal layer, which may be 3, 4, 5, or the like. In someembodiments, metal layers M1 through Mtop are formed of copper usingdamascene processes.

Metal layer 32 is formed over metal layers 24, and may be, or may notbe, electrically coupled to metal lines 26 and vias 28. Metal layer 32may be a blanket layer formed of aluminum, tin, aluminum copper,silicon-containing aluminum copper, or the like. Metal layer 32 may bedeposited over metal layers 24, for example, using physical vapordeposition (PVD). The deposition step of metal layer 32 is performed invacuumed chamber 54. In an exemplary embodiment, the volume percentagesof aluminum and copper in the aluminum copper in metal layer 32 areabout 99.5 percent and about 0.5 percent, respectively. In otherexemplary embodiments, the volume percentages of aluminum, silicon, andcopper in the silicon-containing aluminum copper in metal layer 32 areabout 97.5 percent, about 2 percent, and about 0.5 percent,respectively.

FIG. 1 further illustrates the in-situ formation of blanket protectionlayer 34, which may be formed in-situ with the formation of metal layer32. In some exemplary embodiments, the deposition step of protectionlayer 34 is performed in the same vacuumed chamber 54 for depositingmetal layer 32. Between the step of forming metal layer 32 and the stepof forming blanket protection layer 34, there may not be any vacuumbreak. Accordingly, no oxide is formed on the top surface of metal layer32. In an exemplary embodiment, protection layer 34 is formed using PVD.

Protection layer 34 may be a substantially pure germanium layer, indiumlayer, gold layer, or tin layer. Alternatively, protection layer 34 maycomprise germanium, indium, gold, tin, or alloys thereof. In yet otherembodiments, protection layer 34 may be a composition layer includingtwo or more of a germanium layer, a indium layer, a gold layer, and atin layer that are stacked, and the stacked layers may be repeated. Forexample, protection layer 52 may comprise the stacked layers of Ge/Al,which may be repeated to form Ge/Al/Ge/Al/Ge layers. The materials ofprotection layer 34 are capable of forming a eutectic alloy with thematerial of metal layer 32 and the overlying bond layer 66 (not shown inFIG. 1, please refer to FIG. 5). Accordingly, the material of blanketprotection layer 34 may be selected accordingly to the material of metallayer 32. For example, in the embodiments wherein metal layer comprisesaluminum, the material of protection layer 34 may be selected fromgermanium, indium, gold, or combinations thereof. Alternatively, in theembodiments wherein metal layer 32 comprises tin, protection layer 34may comprise gold. The thickness of protection layer 34 may be less thanabout 500 Å to ensure a reliable bonding (as shown in FIG. 6), and atthe same time no squeezing of the molten eutectic metal occurs.

Referring to FIG. 2, metal layer 32 and protection layer 34 arepatterned using lithography and etching processes. Bond ring 36 isformed from metal layer 32. Accordingly, bond ring 36 may also be formedof aluminum or aluminum copper, although it may also be formed of othermaterials. The remaining portions of protection layer 34 are denoted asprotection layer(s) 52, which are co-terminus with the underlying bondring 36. The edges of protection layer 52 are aligned to the respectiveedge of bond ring 36. Bond ring 36 and protection layer 52 may have aring shape in a top view of the structure shown in FIG. 2. In someembodiments, besides bond ring 36, there are other metal feature 37resulted from the same metal layer 32. The portion of protection layer52 over metal feature 37 may be removed, or may be left un-removed.

Also referring to FIG. 2, MEMS device 38 is formed in the regionencircled by bond ring 36. MEMS device 38 may comprise one or aplurality of capacitors, although it may be another kind of MEMS deviceother than a capacitor. In an exemplary embodiment in which acapacitor(s) is included, MEMS device 38 includes movable element 40 andfixed elements 44 (denoted as 44A, 44B, and 44C). Movable element 40 isalso sometimes referred to as a proof mass. In some embodiments, movableelement 40 and fixed elements 44 are formed of a silicon-containingmaterial(s) such as polysilicon, amorphous silicon, or crystallinesilicon. The silicon-containing material may be doped with a p-type oran n-type impurity to increase the conductivity.

In some embodiments, movable element 40 and fixed elements 44 of MEMSdevice 38 may be grown from metal layer 24 and the overlying structures,if any. In alternative embodiments, MEMS device 38 may be pre-formed onanother wafer, and then bonded to metal layers 24. Fixed elements 44 mayinclude portion 44A, which is under movable element 40 and forms acapacitor with movable element 40. Movable element 40 and fixed elements44 form capacitor plates of the capacitor(s), while air-gaps 48 betweenmovable element 40 and fixed elements 44 form the capacitor insulators.Furthermore, movable element 40 and other fixed elements such as 44Band/or 44C may form additional capacitors, with air-gaps 48 therebetweenforming the capacitor insulators. Although not illustrated, movableelement 40 may be anchored and supported by springs (not shown), whichmay be formed of the same material as that of movable element 40 and/orfixed elements 44. The springs are not in the same plane as illustrated,and hence are not illustrated herein. The springs allow movable element40 to move freely in air-gaps 48, so that the capacitance of thecapacitors formed between movable element 40 and fixed elements 44 maybe changed. The capacitor formed between elements 40 and 44A may be usedfor reflecting the Z-direction movement of movable element, while thecapacitor(s) formed between elements 40 and 44B and 44C may be used forreflecting the movement of movable element 40 in the X and Y directions.

Referring to FIG. 3, anti-stiction coating 60 is formed, for example,using a chemical vapor deposition (CVD) method. Anti-stiction coating 60is formed on the exposed surfaces of movable element 40, fixed elements44 (44A/44B/44C), and protection layer 52. In some embodiments,anti-stiction coating 60 comprises an anti-stiction material, which maycomprises carbon, silicon, fluoride, chloride, and combinations thereof.

A thermal treatment is performed on the structure shown in FIG. 3. Thethermal treatment may be performed at a temperature between about 250°C. and about 450° C. The duration of the thermal treatment may be lessthan about 60 minutes. The thermal treatment may be performed in avacuum environment such as a vacuumed chamber. In alternativeembodiment, a ultra-violet (UV) treatment may be performed.

Referring to FIG. 4, a selective removal is also performed, so that theportions of anti-stiction coating 60 on the surfaces of protection layer52 is removed, while the portions of anti-stiction coating 60 on thesurfaces of movable element 40 and fixed elements 44 may remainun-removed.

Before the formation of anti-stiction coating 60, and also after theselective removal, protection layer 52 may be exposed to open air.Protection layer 52 may also form an oxide (not shown) on its surface.However, the oxide is less stable than the oxide of bond ring 36, whichis prevented from being formed in the embodiments due to the in-situformation of protection layer 52. The oxide of protection layer 52 maybe easily removed in the subsequent bonding process.

FIG. 5 illustrates the bonding of cap 64 onto the structure shown inFIG. 3. In an embodiment, cap 64 may be formed of a semiconductormaterial such as silicon, a metal, or a dielectric material. Cap 64includes a portion over MEMS device 38, with an air-gap between cap 64and MEMS device 38. Bond layer 66 is formed as a bottom surface portionof cap 64, and will be joined with bond ring 36 and protection layer 52.In a top view, bond layer 66 may have a ring that has a size and a shapematching the top-view size and the shape, respectively, of bond ring 36.In some embodiments, cap 64 may include additional MEMS devices (notshown), CMOS devices (not shown), or the like. In an embodiment, bondlayer 66 comprises a material that forms a eutectic alloy withprotection layer 52 and bond ring 36. Accordingly, bond layer 66 maycomprise germanium, indium, tin, gold, or the like, and may have asingle-layered structure or a composite structure.

The bonding of cap 64 to bond ring 36 and protection layer 52 may beperformed in chamber 68. During the bonding process, forming gas 70 maybe pumped in, and purged from, chamber 68. Forming gas 70 may comprise areduction gas such as hydrogen (H₂) or an acid such as oxalic acid oracetic acid. Accordingly, the oxide of protection layer 52 and bondlayer 66 will be removed before and during the bonding process. Thebonding process may be performed at a temperature between about 420° C.and about 460° C., for example, when the aluminum and germanium areinvolved in the bonding. The bonding temperature, depending from thetype of the resulting eutectic alloy, may also be higher or lower.During the bonding process, a force may be applied to press cap 64against bond ring 36 and protection layer 52. FIG. 6 illustrates theresulting structure. At least a top layer of bond ring 36 forms eutecticalloy 72 with protection layer 52 and bond layer 66 as shown in FIG. 5.During the bonding process, protection layer 52, bond layer 66, and atleast the top layer of bond ring 36 go through a eutectic reaction, andare liquefied to form eutectic alloy 72 at a high temperature. Theliquid is solidified when the temperature is lowered. Eutectic alloy 72may also have a ring shape in the top view of FIG. 6. Cap 64 is thusjoined with bond ring 36.

In the embodiments shown in FIGS. 1 through 6, MEMS devices are formedover substrate 20, with active devices 22 formed thereon. Accordingly,the structure shown in FIG. 6 comprises both active devices 22 and MEMSdevice 38. In alternative embodiments, no active device is formed on thesurface of substrate 20. FIGS. 7 through 12 illustrate the formationprocess of the respective structure in accordance with variousalternative embodiments. Unless specified otherwise, the materials andformation methods of the components in these embodiments are essentiallythe same as the like components, which are denoted by like referencenumerals in the embodiment shown in FIGS. 1 through 6. The formationdetails of the embodiment shown in FIGS. 7 through 12 may thus be foundreferring to the discussion of the embodiments shown in FIGS. 1 through6.

In these embodiments, metal layer 32 may be formed on dielectric layer74 (FIG. 7), which may be a silicon oxide form, by thermal oxidizing asurface layer of silicon substrate 20. Alternatively, substrate 20 is adielectric substrate, and bond ring 36 may be formed directly ondielectric substrate 20. The formation process may include the in-situdeposition of metal layer 32 and blanket protection layer 34 (FIG. 7),with no vacuum break between the deposition steps of metal layer 32 andblanket protection layer 34. Furthermore, metal layer 32 and blanketprotection layer 34 may be formed in the same process chamber 54, andmay be formed using PVD. Metal layer 32 and the blanket protection layer34 are then patterned using a lithography and etching process, and theresulting structure is illustrated in FIG. 8. FIG. 8 also shows theformation of MEMS device 38. The remaining process steps and therespective materials, including the formation of anti-stiction coating60 and the bonding of cap 64 through bond layer 66, are shown in FIGS. 9through 12, and are essentially the same as shown in FIGS. 2 through 5.The process details and the materials may be found by referring to theembodiments shown in FIGS. 1 through 6, and are not repeated herein.

In the embodiments, by in-situ forming bond ring 36 and protection layer52, protection layer 52 prevents the oxidation of bond ring 36.Accordingly, there is no need to perform an ion bombardment to removethe resulting oxide. The adverse effects of the ion bombardment are thusavoided, which adverse effects include the charging of the movableelement and the fixed elements, and in turn the increase in thepossibility of the stiction.

In accordance with embodiments, a method includes forming a MEMS device,forming a bond layer adjacent the MEMS device, and forming a protectionlayer over the bond layer. The steps of forming the bond layer and theprotection layer include in-situ deposition of the bond layer and theprotection layer.

In accordance with other embodiments, a method includes forming a MEMSdevice over a substrate. The step of forming the MEMS device includesforming a movable element as a first capacitor plate of a capacitor, andforming a fixed element as a second capacitor plate of the capacitor.The method further includes depositing a metal layer over the substratein a process chamber, and depositing a protection layer over the metallayer and in the process chamber. Between the step of depositing themetal layer and the step of depositing the protection layer, no vacuumbreak occurs to the process chamber. The metal layer and the protectionlayer are patterned to form a bond ring encircling the MEMS device. Acap is bonded to cover the MEMS device, wherein during the step ofbonding, the protection layer forms a eutectic alloy with the bond ringin a eutectic reaction.

In accordance with yet other embodiments, a device includes a substrate,and a MEMS device over the substrate. The MEMS device includes a movableelement as a first capacitor plate of a capacitor, and a fixed elementas a second capacitor plate of the capacitor. A bond ring encircles theMEMS device and comprises a metal. A protection layer is disposed overthe bond ring, wherein the protection layer is capable of forming aeutectic metal with the bond ring.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: forming amicro-electro-mechanical system (MEMS) device; forming a first bondlayer adjacent the MEMS device; and forming a protection layer over thefirst bond layer, wherein the steps of forming the first bond layer andthe protection layer comprise in-situ deposition of the first bond layerand the protection layer.
 2. The method of claim 1, wherein the steps offorming the first bond layer and the protection layer comprise:depositing a blanket metal layer; depositing a blanket protection layer,wherein the blanket metal layer and the blanket protection layer aredeposited in a same process chamber; and patterning the blanket metallayer and the blanket protection layer to form the first bond layer andthe protection layer, respectively.
 3. The method of claim 2, whereinbetween the step of depositing the blanket metal layer and the step ofdepositing the blanket protection layer, no vacuum break occurs.
 4. Themethod of claim 1 further comprising bonding a cap to cover the MEMSdevice, wherein during the step of bonding, the protection layer forms aeutectic alloy with the first bond layer.
 5. The method of claim 4,wherein during the step of bonding, a second bond layer of the cap formsthe eutectic alloy with the protection layer and the first bond layer ina eutectic reaction.
 6. The method of claim 1, wherein the protectionlayer comprises a material selected from the group consistingessentially of germanium, indium, gold, and combinations thereof.
 7. Themethod of claim 1 further comprising: after the step of forming theprotection layer, forming an anti-stiction coating comprising a firstportion on a movable element of the MEMS device, and a second portion onthe protection layer; and removing the second portion of theanti-stiction coating, wherein the first portion of the anti-stictioncoating is not removed.
 8. A method comprising: forming amicro-electro-mechanical system (MEMS) device over a substrate, whereinthe step of forming the MEMS device comprises: forming a movable elementas a first capacitor plate of a capacitor; and forming a fixed elementas a second capacitor plate of the capacitor; depositing a metal layerover the substrate in a process chamber; depositing a protection layerover the metal layer and in the process chamber, wherein between thestep of depositing the metal layer and the step of depositing theprotection layer, no vacuum break occurs to the process chamber;patterning the metal layer and the protection layer to form a bond ringencircling the MEMS device; and bonding a cap to cover the MEMS device,wherein during the step of bonding, the protection layer forms aeutectic alloy with the bond ring in a eutectic reaction.
 9. The methodof claim 8, wherein the protection layer is in contact with the metallayer.
 10. The method of claim 8, wherein the protection layer is astacked layer comprising a plurality of layers formed of differentmaterials.
 11. The method of claim 8, wherein the cap comprises a bondlayer on a surface of the cap, and wherein during the step of bonding,the bond layer of the cap forms the eutectic alloy with the protectionlayer and the bond layer in the eutectic reaction.
 12. The method ofclaim 11, wherein the bond layer comprises a material selected from thegroup consisting essentially of germanium, indium, gold, andcombinations thereof.
 13. The method of claim 12, wherein the protectionlayer comprises a material selected from the group consistingessentially of germanium, indium, gold, and combinations thereof. 14.The method of claim 8 further comprising: after the step of forming theprotection layer, forming an anti-stiction coating comprising a firstportion on the movable element of the MEMS device, and a second portionon the protection layer; and removing the second portion of theanti-stiction coating, wherein the first portion of the anti-stictioncoating is not removed.
 15. A device comprising: a substrate; amicro-electro-mechanical system (MEMS) device over the substrate,wherein the MEMS device comprises: a movable element as a firstcapacitor plate of a capacitor; and a fixed element as a secondcapacitor plate of the capacitor; a bond ring encircling the MEMSdevice, wherein the bond ring comprises a metal; and a protection layerover the bond ring, wherein the protection layer is capable of forming aeutectic metal with the bond ring.
 16. The device of claim 15, whereinthe protection layer is in contact with the bond ring.
 17. The device ofclaim 15, wherein edges of the protection layer are co-terminus withrespective edges of the bond ring.
 18. The device of claim 15 furthercomprising a cap comprising a bond layer at a surface, wherein the bondlayer comprises a material capable of forming a eutectic alloy with theprotection layer and the bond ring, and wherein the cap comprises a ringhaving substantially a same size as the bond ring.
 19. The device ofclaim 15, wherein the protection layer comprises a material selectedfrom the group consisting essentially of germanium, indium, gold, andcombinations thereof, and wherein the bond ring comprises a materialselected from the group consisting essentially of aluminum and tin. 20.The device of claim 15, wherein the protection layer is a stacked layercomprising a germanium layer stacked on an aluminum layer.